Applications of the first law

Introduction:

Thermodynamics is a branch of physics and chemistry that deals with the energy and work produced or available in a system. This branch of physics deals only with the large-scale response of a system that can be observed and measured in experiments effortlessly whereas if we talk about the small-scale gas interactions, they are described by the Kinetic theory of Gases. There are three principal laws of thermodynamics, which are described in detail below.

Laws of Thermodynamics :

As described above, there are three laws of thermodynamics. Let us look at some overview of these three laws.

First Law of Thermodynamics:

The first law of thermodynamics is also known as the law of conservation of energy. The first law states that energy can neither be created nor be destroyed but can be converted from one form to another. It can be mathematically defined as ΔQ = ΔU + ΔW where, ΔQ stands for heat provided or lost in the process. ΔU stands for change in the internal energy because of the change in heat. ΔW stands for the work done during the process. Note:- In some places you might notice a change in the sign in the above equation. No need to panic as both the equations are correct, and they say the same thing. The reason for the difference is that in the formula ΔQ = ΔU + ΔW we are assuming that W represents the work done on the system, and when we use ΔQ = ΔU – ΔW we are assuming that W represents the work done by the system. Because of the difference in the work done, the sign of the equation changes.

Second Law of Thermodynamics:

The Second Law of Thermodynamics is commonly known as the Law of Increased Entropy. While the quantity of energy remains the same as per the first law of thermodynamics, the quality of matter or energy deteriorates gradually over time. This law can also be considered as the most important law of thermodynamics as it includes entropy, which dictates whether a process or a reaction will be spontaneous or not. Mathematically, the second law of thermodynamics is represented as; ΔSuniv > 0 where ΔSuniv is the change in the entropy of the universe.

Third Law of Thermodynamics:

The third law of thermodynamics states that as the temperature approaches absolute zero (0 K), the entropy of a system approaches a constant (and minimum) value. In this way, the third law provides an absolute reference point for the determination of entropy of any substance. The third law also says that it is not possible for any system to reach absolute zero in a finite number of steps. As we mentioned absolute 0K temperature, so what does absolute 0 K temperature mean? The third law of thermodynamics states that as the temperature approaches absolute zero (0 K), the entropy of a system approaches a constant (and minimum) value. In this way, the third law provides an absolute reference point for the determination of entropy of any substance. The third law also says that it is not possible for any system to reach absolute zero in a finite number of steps. As we mentioned absolute 0 K temperature, so what does absolute 0 K temperature mean? Absolute 0 K temperature can be termed as the temperature at which all particle motion almost stops. The temperature is known as absolute zero, and it is the lowest possible temperature. It is equal to -273.15 degrees Celsius, -459.67 degrees Fahrenheit, and 0 Kelvin.

Applications of First Law of Thermodynamics:

We went through an overview of what the laws of thermodynamics are, now, let us see what are the applications of the First Law of Thermodynamics. As we all know, the first law of thermodynamics talks about the conservation of energy. Therefore, the applications of the first law of thermodynamics are differentiated into 4 purposes: 1:- Isolated Process: As the name proposes, it is a process that does not interact with the surroundings. Because the system is isolated, there is no heat loss and thus, no work is done. Therefore, the internal energy of an isolated system remains constant and thus, no energy is destroyed in any of the stages of the process. 2:- A Cyclic Process: As the name proposes, this is a process where the system returns to its original state after passing all the intermediate stages. Just like the isolated process, in this process also the change in internal energy is zero thus, no energy is destroyed. 3:- Boiling Process: When a liquid is heated, it absorbs heat and the temperature of the liquid thus rises. After some time, a stage is reached by the liquid, when it starts boiling and changes its phase from liquid to vapour. Due to this change of phase from liquid to vapour, the volume increases and work is done. As the process involves work and heat, the first law of thermodynamics can be applied. In this process, internal energy changes and gets converted from one form to the other without getting destroyed, fulfilling all the conditions of the first law of thermodynamics. 4:- Melting Process: When the quantity of heat Q is given to a solid at its melting point, it is converted into liquid. The temperature and pressure remain constant till the whole solid is completely converted into liquid. The internal energy changes during melting, therefore the first law of thermodynamics can be applied here as well. Just like the boiling process, in this process, internal energy changes and gets converted from one form to the other without getting destroyed, fulfilling all the conditions of the first law of thermodynamics. The only difference between the last two processes is the temperature to which the internal energy changes. On one hand, the liquid changes to vapour as an effect of the rise in internal energy, and on the other hand, the liquid changes to a solid phase as a result of the negative change in heat energy.

Conclusion:

Now, we hope you know almost everything about the laws of thermodynamics and the applications of the first law of thermodynamics. Thermodynamics is a very vast topic, and we aim to provide you very detailed information in the easiest way possible.